ABSTRACT

Effects of a submerged dike on the statistical properties of simulated random waves were studied experimentally. Deep water waves were generated mechanically by a computer controlled piston type wave generator according to the target JONSWAP spectrum. The variations of the surface elevations before and after the waves passing over the dike were measured. Possible changes of the spectral shapes and the probability distributions of wave heights and surface elevations were analyzed. Except for the possible energy loss due to the wave shoaling and breaking, the present results indicate that wave statistics will not be essentially (seriously) affected by the presence of the dike.

INTRODUCTION

Random wave fields are often treated as the combinations of denumerably many independent harmonic components, with their own frequencies and wavelengths, and thus travels freely on the water surface. Most of our present wave spectral models are based upon this assumption. Neglecting the wave-wave interaction, Phillips (1958), for example, derived his famous −5 power law by assuming that the only dominant factor for wave energy dissipation in deep water is through wave breaking. Later, Pierson & Moskowitz (1964) utilized this argument and celebrated the Pierson-Moskowitz (P-M) spectrum for fully developed seas. For developing wind sea, the modified P-M spectrum, i.e., the JONSWAP spectrum, due to Hasselmann et al. (1973) is now widely used. On the other hand, for the deterministic wave statistics, Longuet-Higgins (1952) derived the first theoretical base theory with an additional assumption of narrow-bandedness. When a group of free waves propagates from deep to shallower waters, the longer waves will subject to the effects of shoaling, partial reflection, as well as eventual breaking; while the shorter waves will be relatively unaffected by the underlying topographical conditions.

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